True, my sister is celiac and it is less common than today's diets would seem to want people to think. But as I understand it gluten is an indigestible protein that has been rising in concentration as we have been breeding wheat and genetically modifying wheat to be more productive. I believe the concentration of gluten in modern wheat is 10x that of the heirloom or ancient grain versions... Not sure what my point is
I think your point is that farmers preferred to plant higher gluten wheat and rye because it was easier to make bread out of it. Almost all of our crop plants are significantly different than both their wild ancestors and their forms from two or three thousand years ago. That is sort of the point of agriculture - to allow more people to stay in one place and eat than hunting and gathering.